I am building a 12'x16' pergola. I was planning on using 6"x6" posts to give the whole thing a beefier look and feel. It's very windy where I live, as well, and I want this structure to be able to withstand the elements. Would four posts be sufficient? Or should I plan on 6 posts, with three along the 16' side? I was planning on using 2"x6" beams connected to these posts.
I'm not planning on covering the pergola, so any snow or rain won't be accumulating on the top of it.
For that size (12' x 16') pergola three posts per side would be appropriate to give it a better look, since you are going to have open rafters the only reason to use three is for great symmetry to the eye.
The 2x6 will do fine for the 12' rafters but keep in mind that 6x6 posts with anything smaller running on top (beams) will make the whole thing look not substantial.
You also didn't mention if you plan on having knee braces, they also give the look and feel of substantial building, as well as beam to post connection additional support. (this really isn't an issue with a pergola but would be more for looks)
Timber framing usually has all the main members sized to each other and the load that will be carried.
With 6x6 posts I would use 6x6 main beams and fasten with 3" x 5" centered blind (leave the top of the mortise closed instead of through) mortise and tenon joints.
I'd be using 9'x6"x6" posts for mine. The pergola in this photo is, of course, using just four 10'x4"x4" posts. Otherwise, mine would be much the same. 2"x6" beams (I hope I'm using that term correctly) across the long side of the structure, two of those on each side. I'd then use 13'x2"x6" rafters, probably spaced out every foot and a half or so. And then again across the long end on top I'd use 17'x2"x4" wood, just like they're using in that photo.
I'd definitely want to add the knee braces, like on this one. I think i'll be planning on notching all these timbers together, as well. I like pergola look when they are notched together (unlike this one).
You might do just fine with 5 posts, 3 on the back side of the pergola, and then 2 on the front side ---- it would give that side a more open and welcoming feel.
My brothers and I just built a heavy pergola for my parents in January. We used all pressure treated timber, with 6 x 6 posts, and 2' x 12' x 20' stringers for the long boards. The slats running perpendicular to those long stringers were 2 x 10 x 10'. Final dimension of the top was 10' x 20'. It's beefy. I only used 4 posts.
More important, in my opinion, than the # of posts (4, 5, or 6) is that you have some diagonal bracing to keep it from rocking or racking. We ordered 2 extra 6 x 6 posts, and I cut those down so I could use them as my diagonal braces. They attach to the posts at a 45 degree angle and are screwed into the long 2 x 12 runners. Not only do them make the structure rock solid (you can't get it to budge or wiggle in any direction), but they give the structure a cool architectural look, like a post & beam craftsman home.
"The rule of no realm is mine. But all worthy things that are in peril as the world now stands, these are my care. And for my part, I shall not wholly fail in my task if anything that passes through this night can still grow fairer or bear fruit and flower again in days to come. For I too am a steward. Did you not know?" Gandolf
posted 3 years ago
Thanks for the input, Marco. You gave me some good ideas.